On Tue, Jun 19, 2018 at 10:40:08PM +1000, Michael Ellerman wrote: > Ram Pai <linux...@us.ibm.com> writes: > > Applications need the ability to associate an address-range with some > > key and latter revert to its initial default key. Pkey-0 comes close to > > providing this function but falls short, because the current > > implementation disallows applications to explicitly associate pkey-0 to > > the address range. > > > > Lets make pkey-0 less special and treat it almost like any other key. > > Thus it can be explicitly associated with any address range, and can be > > freed. This gives the application more flexibility and power. The > > ability to free pkey-0 must be used responsibily, since pkey-0 is > > associated with almost all address-range by default. > > > > Even with this change pkey-0 continues to be slightly more special > > from the following point of view. > > (a) it is implicitly allocated. > > (b) it is the default key assigned to any address-range. > > (c) its permissions cannot be modified by userspace. > > > > NOTE: (c) is specific to powerpc only. pkey-0 is associated by default > > with all pages including kernel pages, and pkeys are also active in > > kernel mode. If any permission is denied on pkey-0, the kernel running > > in the context of the application will be unable to operate. > > We could fix that by saving/restoring the AMR when we come into the > kernel, and switching to a kernel-AMR with all keys accessible. > > We'd then need to think about copy_to/from_user() gup etc. So maybe we > don't want to do that. But it's not set in stone. > > Are we calling this a bug fix?
Actually, I call it borderline bug fix. Its more of a feature. RP
